Habitually consuming caffeine in coffee and other drinks and foods may protect against atrial fibrillation, a meta-analysis suggested.

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Habitually consuming caffeine in coffee and other drinks and foods may protect against atrial fibrillation.

Point out that although a cause-and-effect relationship cannot be established, the authors speculated that caffeine might protect against atrial fibrillation through its anti-fibrotic effect.

Habitually consuming caffeine in coffee and other drinks and foods may protect against atrial fibrillation, a meta-analysis suggested.

In pooled results from studies with adjustment for potential confounders, the risk of atrial fibrillation was lower with consumption of both low doses of caffeine (RR 0.89, 95% CI 0.80-0.99) and high doses (RR 0.84, 95% CI 0.75-0.94), according to Dongfeng Gu, MD, PhD, of Fu Wai Hospital in Beijing, and colleagues.

In a dose-response analysis, the risk of incident atrial fibrillation was lower by a relative 6% for each increase in habitual caffeine intake of 300 mg/day (RR 0.94, 95% CI 0.90-0.99), they reported online in the Canadian Journal of Cardiology.

The researchers cautioned, however, that "there is a history of misleading large cohort studies in the cardiovascular literature, including the ultimately proven-to-be-false reports of estrogens, vitamin E, vitamin C, amongst others as being 'cardioprotective.'"

The current meta-analysis included six prospective cohort studies with a total of 228,465 participants. Three were conducted in the U.S., two in Sweden, and one in Denmark. Caffeine consumption was determined based on daily coffee consumption in three studies and on consumption of coffee, tea, cola, cocoa, or chocolate in the other three.

The amount of caffeine in a cup of coffee varied by geographical location: 140 mg for the U.K. and Northern Europe, 50 mg for Southern Europe, and 85 mg for the U.S.

Low caffeine intake was considered less than 500 mg/day and high intake was more than that.

During an average follow-up that ranged from 4 to 25.2 years across the studies, 1.9% of the participants developed atrial fibrillation or had it recorded (participants were confirmed free of the arrhythmia at baseline in only four of the studies).

In the primary meta-analysis, caffeine consumption was not significantly associated with atrial fibrillation (RR 0.90, 95%CI 0.81-1.01), although the inverse association became significant in an analysis of studies with minimal comparability bias (greater adjustment for potential confounders).

Although a cause-and-effect relationship cannot be established, Gu and colleagues speculated that caffeine might protect against atrial fibrillation through its anti-fibrotic effect.

"There were several studies [that] showed that caffeine reduced hepatic fibrosis ... by interfering with transforming growth factor beta signaling," they wrote. "Though there are few studies evaluating the anti-fibrosis effect of caffeine on the heart, it is possible that caffeine also prevents cardiac fibrosis."

Protection also "might be related to co-occurring phytochemicals because caffeine is normally consumed in the form of plant-derived products and extracts that invariably contain other potentially bioactive phytochemicals."

The authors acknowledged that the analysis was limited by the potential underestimation of incident atrial fibrillation, the use of self-reported caffeine intake, the inability to adjust for some potential confounders, such as sleep apnea, and the relatively small number of atrial fibrillation events in the included studies.

"The result should be eventually confirmed in a randomized clinical trial ideally," they wrote. "But due to [the] long follow-up duration and large sample size needed to detect [a] beneficial effect of caffeine consumption, it will be very tough to conduct such a randomized placebo-controlled study."

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